In recent years, the capacity of an optical disc increases conspicuously as an information amount to be handled increases. For example, whereas the capacity was 2.6 GB/face in the case of a DVD-RAM of the first generation, as a result of efforts for technology development such as shorter wavelength of a laser to be used and a higher NA of a lens, the capacity of 25 GB/face has been realized in the case of a blue-ray disc. Further, research and development in the technology of increasing an area density in order to record a larger amount of information and the technology of increasing a capacity by the multi-layering of an information face has been advancing. For example, a record reproduction technology for realizing the capacity of 50 GB per face is described in International Symposium on Optical Memory 2004, Technical Digest, Tu-C-02, p22. Further, as an example of the technologies of increasing a capacity by the multi-layering of an information face, a technology for realizing the capacity of 150 GB by stacking six information faces, each of which has the capacity of 25 GB, in layers is described in International Symposium on Optical Memory 2004, Technical Digest, We-E-02, p52. In addition, as an example of discs having a larger capacity, the structure of a multilayered disc having information faces in two or more layers is described in JP-A No. 74742/2002.
With the advancement of the capacity increasing technologies such as the increase of an area density and multi-layering, the research and development of record reproduction technologies is also advancing. As a means of recording information on an optical disc with a high degree of accuracy, there is the adaptive type recording waveform control technology. The adaptive type recording waveform control technology is a method of changing a recording pulse width when a recording mark is formed and is described, for example, on p. 95 of the proceedings of the 11th Symposium on Phase Change Optical Information Storage in 1999. The method is the one wherein information is recorded by increasing or decreasing a recording pulse shape within a length shorter than a clock unit in accordance with the preceding space and/or the succeeding space, and the method makes it possible to suppress to the utmost the edge shift caused by thermal interference in the track direction that is derived from the fact that a recording mark and a space are smaller than a light spot, is very effective in mark edge recording, and exhibits an effect in high area density recording wherein the thermal interference is substantial.
Meanwhile, JP-A No. 63586/2005 (corresponding to US 2005/105438) describes a method of introducing a downward pulse immediately before a recording mark in order to reduce thermal interference generated at the time of high-speed recording. The write strategy of the patent document is shown in FIG. 11A. Further, JP-A No. 295440/1994 (corresponding to U.S. Pat. No. 5,490,126) describes a method of suppressing thermal interference by irradiating the leading and trailing edges of a short space with read power. The write strategy of the patent document is shown in FIG. 11B.
As a recording method conforming to multi-layering, JP-A No. 178448/2003 (corresponding to US 2003/081523) describes the method of recording good signals by using a recording pulse that makes the temperature change of a recording layer caused by the condensation of an optical beam be on the side of rapid cooling in terms of time more in an information recording layer close to the incidence of light than in the information recording layer farthest from the incidence of the light.